Academia.eduAcademia.edu

Figure 18 – uploaded by Rainer Martini

See full PDFdownloadDownload figure
Fig. 18. Conduction band profile of two periods (active region + injector) of far-IR (A = 24 jxm) AlInAs/GalnAs quantum cascade laser under an applied electric field of 15 kV/cm. The layer thicknesses in nanometers of a single stage are, from left to right starting from the injection barrier (indicated by an arrow): 2.4/6.4/ 1.6 /6.8/1.4/7.0/1.2 /7.0/1.45 /7.7/ 0.4/9.7/0.35 /10.7/ 0.45/11.9. AllnAs layers are in bold. The underlined layers are n-type doped to n= 2 x 1017 cm—*. The moduli squared of the wave-functions of each state of the miniband are shown. Wavy arrows indicate the lasing transition. The laser radiation travels parallel to the layers and is TM polarized.

Figure 18 Conduction band profile of two periods (active region + injector) of far-IR (A = 24 jxm) AlInAs/GalnAs quantum cascade laser under an applied electric field of 15 kV/cm. The layer thicknesses in nanometers of a single stage are, from left to right starting from the injection barrier (indicated by an arrow): 2.4/6.4/ 1.6 /6.8/1.4/7.0/1.2 /7.0/1.45 /7.7/ 0.4/9.7/0.35 /10.7/ 0.45/11.9. AllnAs layers are in bold. The underlined layers are n-type doped to n= 2 x 1017 cm—*. The moduli squared of the wave-functions of each state of the miniband are shown. Wavy arrows indicate the lasing transition. The laser radiation travels parallel to the layers and is TM polarized.

Related Figures (22)

Fig. 2. (a) High-frequency modulation response traces of a 8-jm QC laser at 20 K, for different values of the drive current ranging from very near threshold (150 mA), up to over one order of magnitude higher photon density (400 mA). These traces were normalized to the experimental frequency response of the receiver and reflect only the modulation response of the QC laser. (b) High- frequency modulation response of a different laser, for a set of values of the laser bias, at 80 K.
Fig. 2. (a) High-frequency modulation response traces of a 8-jm QC laser at 20 K, for different values of the drive current ranging from very near threshold (150 mA), up to over one order of magnitude higher photon density (400 mA). These traces were normalized to the experimental frequency response of the receiver and reflect only the modulation response of the QC laser. (b) High- frequency modulation response of a different laser, for a set of values of the laser bias, at 80 K.
Fig. 3. Observed transmitter eye diagram of the QC laser (a) at 20 K and (b) at 85 K.
Fig. 3. Observed transmitter eye diagram of the QC laser (a) at 20 K and (b) at 85 K.
Fig. 4. Measured bit error rate as a function of attenuation of the transmitted laser beam.
Fig. 4. Measured bit error rate as a function of attenuation of the transmitted laser beam.
Fig. 5. Schematic view of the optical and electrical setup for the free-space indoor audio/video transmission.
Fig. 5. Schematic view of the optical and electrical setup for the free-space indoor audio/video transmission.
Fig. 6. Section (250 x 100 pixel) of a captured television picture after trans- mission (upper part) and the original picture (lower part), using the setup of Fig. 5.
Fig. 6. Section (250 x 100 pixel) of a captured television picture after trans- mission (upper part) and the original picture (lower part), using the setup of Fig. 5.
Fig. 7. Schematics of the optical and electrical setups of the optical wire- less transmission link. The ~100-m path is between two buildings at Bell Laboratories, Murray Hill, NJ.
Fig. 7. Schematics of the optical and electrical setups of the optical wire- less transmission link. The ~100-m path is between two buildings at Bell Laboratories, Murray Hill, NJ.
Fig. 8. (a) The signal at the output of the LNB (dashed) together with the signal after transmission over the free-space link (solid line) of Fig. 7. (b) Television screenshot.
Fig. 8. (a) The signal at the output of the LNB (dashed) together with the signal after transmission over the free-space link (solid line) of Fig. 7. (b) Television screenshot.
Fig. 9. Comparison of the received intensities of the mid-IR (\ = 8.1 j«m) and the near-IR (\ = 0.85 jm) link as a function of time. Fog came up around 2 AM and progressively dissipated during the measurement. The inset is a logarithmic plot of the ratio of the two curves in the main graph and represents the time evolution of the difference of the optical losses at the two wavelengths as the structure of the fog changes.
Fig. 9. Comparison of the received intensities of the mid-IR (\ = 8.1 j«m) and the near-IR (\ = 0.85 jm) link as a function of time. Fog came up around 2 AM and progressively dissipated during the measurement. The inset is a logarithmic plot of the ratio of the two curves in the main graph and represents the time evolution of the difference of the optical losses at the two wavelengths as the structure of the fog changes.
Fig. 10. (a) Oscilloscope trace of a typical pulse generated by a gain-switched QC laser at \ ~ 8 xm; (b) Optical spectra of a QC laser output, at constant dc bias for different values of the RF drive frequency 1, showing modelocking when v equals the frequency separation between the longitudinal modes.
Fig. 10. (a) Oscilloscope trace of a typical pulse generated by a gain-switched QC laser at \ ~ 8 xm; (b) Optical spectra of a QC laser output, at constant dc bias for different values of the RF drive frequency 1, showing modelocking when v equals the frequency separation between the longitudinal modes.
Fig. 11. Illustration of saturable absorption mechanism leading to passive mode-locking in QC lasers. The refractive index profile and resulting intensity distribution of the fundamental waveguide mode along the lateral direction (parallel to the active layer) is shown, along with a cross section of the laser waveguide. Self-focusing occurs in the lateral direction due to the strong refractive index nonlinearity (optical Kerr effect) of the active region associated with the intersubband optical transition: if the intensity increases (going from the dashed to the continuous curves), the index near the center of the waveguide increases, and the beam is correspondingly more tightly confined. As a result, light absorption associated with the penetration of the mode in the metallic regions saturates with increasing intensity.
Fig. 11. Illustration of saturable absorption mechanism leading to passive mode-locking in QC lasers. The refractive index profile and resulting intensity distribution of the fundamental waveguide mode along the lateral direction (parallel to the active layer) is shown, along with a cross section of the laser waveguide. Self-focusing occurs in the lateral direction due to the strong refractive index nonlinearity (optical Kerr effect) of the active region associated with the intersubband optical transition: if the intensity increases (going from the dashed to the continuous curves), the index near the center of the waveguide increases, and the beam is correspondingly more tightly confined. As a result, light absorption associated with the penetration of the mode in the metallic regions saturates with increasing intensity.
Fig. 13. Absorption profile for N2O plotted on an absorbance scale. The arrow that is off the molecular resonance shows the region where the intensity fluctuations are measured whereas the arrow on the side of the molecular resonance corresponds to the region where the frequency fluctuations are measured. The thick segment represents the region of the profile that is used to determine the frequency-to-intensity conversion factor. Fig. 12. (a) Optical spectra of a \ = 8-m QC laser under conditions of SML for different values of the laser dc bias. Inset: Linear autocorrelation trace of the same laser taken with a Fourier transform interferometer showing pulsed emission with a repetition rate equal to the radiation round trip frequency v, in the laser. (b) RF spectrum, peaked at v.., of the photocurrent generated by the same laser in a high-speed quantum-well IR detector, measured with a 1-kHz resolution bandwidth. (c) Far-field beam profiles under CW and SML operation from a \ = 8 ym device (exhibiting nonself-starting modelocking), versus emission angle in the lateral direction. The beam narrowing in the SML case indicates self-focusing.
Fig. 13. Absorption profile for N2O plotted on an absorbance scale. The arrow that is off the molecular resonance shows the region where the intensity fluctuations are measured whereas the arrow on the side of the molecular resonance corresponds to the region where the frequency fluctuations are measured. The thick segment represents the region of the profile that is used to determine the frequency-to-intensity conversion factor. Fig. 12. (a) Optical spectra of a \ = 8-m QC laser under conditions of SML for different values of the laser dc bias. Inset: Linear autocorrelation trace of the same laser taken with a Fourier transform interferometer showing pulsed emission with a repetition rate equal to the radiation round trip frequency v, in the laser. (b) RF spectrum, peaked at v.., of the photocurrent generated by the same laser in a high-speed quantum-well IR detector, measured with a 1-kHz resolution bandwidth. (c) Far-field beam profiles under CW and SML operation from a \ = 8 ym device (exhibiting nonself-starting modelocking), versus emission angle in the lateral direction. The beam narrowing in the SML case indicates self-focusing.
Fig. 14. Time-series measurements of: (a) detector/preamplifier noise floor measured when the laser is blocked; (b) laser intensity fluctuations measured when the laser is tuned off of the molecular resonance; and (c) frequency fluctuations measured when the laser is tuned to the side of the molecular resonance. All panels have identical vertical axis scaling. The right vertical axis in (c) also plots the relative frequency fluctuations, which are obtained by using the conversion factor.
Fig. 14. Time-series measurements of: (a) detector/preamplifier noise floor measured when the laser is blocked; (b) laser intensity fluctuations measured when the laser is tuned off of the molecular resonance; and (c) frequency fluctuations measured when the laser is tuned to the side of the molecular resonance. All panels have identical vertical axis scaling. The right vertical axis in (c) also plots the relative frequency fluctuations, which are obtained by using the conversion factor.
Fig. 15. Frequency noise spectral density normalized to a 1-Hz bandwidth and plotted on a bilogarithmic scale. Dashed line: the detector/preamplifier noise floor (5 pA/,/Hz).
Fig. 15. Frequency noise spectral density normalized to a 1-Hz bandwidth and plotted on a bilogarithmic scale. Dashed line: the detector/preamplifier noise floor (5 pA/,/Hz).
Fig. 16. Setup forthe stabilization of QC lasers using the Pound- Dreaver- Hall technique. This method locks the frequency of the laser to the center of a cavity resonance.
Fig. 16. Setup forthe stabilization of QC lasers using the Pound- Dreaver- Hall technique. This method locks the frequency of the laser to the center of a cavity resonance.
Fig. 17. Heterodyne beat between two cavity-locked QC lasers as recorded with a FFT spectrum analyzer. The width of the central feature represents th: quadrature sum of the individual linewidths of each laser. A nalysis of this central feature at lower resolution bandwidth yields a full-width-at- half-maximum of 5. Hz. Additional features spaced evenly by about 2 kHz result from an acousto-mechanical resonance within the piezo-controlled cavity that could not be removed
Fig. 17. Heterodyne beat between two cavity-locked QC lasers as recorded with a FFT spectrum analyzer. The width of the central feature represents th: quadrature sum of the individual linewidths of each laser. A nalysis of this central feature at lower resolution bandwidth yields a full-width-at- half-maximum of 5. Hz. Additional features spaced evenly by about 2 kHz result from an acousto-mechanical resonance within the piezo-controlled cavity that could not be removed
Fig. 19. Normalized intensity profile of the fundamental optical mode com- puted for: (a) a quantum cascade laser dielectric waveguide and (b) a surface plasmon waveguide designed for a wavelength of 24 4m. The shaded areas indicate the stack of active regions and injectors. In the dielectric case, the thickness of the epitaxially grown material is 14 jm. The origin of the abscisse is at the air- semiconductor interface. In the surface plasmon case, the thickness is instead 6.5 jzm. The optical confinement factor is indicated by T, and the computed waveguide losses are 41 cm—+ for both waveguides.
Fig. 19. Normalized intensity profile of the fundamental optical mode com- puted for: (a) a quantum cascade laser dielectric waveguide and (b) a surface plasmon waveguide designed for a wavelength of 24 4m. The shaded areas indicate the stack of active regions and injectors. In the dielectric case, the thickness of the epitaxially grown material is 14 jm. The origin of the abscisse is at the air- semiconductor interface. In the surface plasmon case, the thickness is instead 6.5 jzm. The optical confinement factor is indicated by T, and the computed waveguide losses are 41 cm—+ for both waveguides.
Fig. 21. Pulsed light output versus current characteristic of a \ = 24 «xm QC laser at various heat sink temperatures and voltage- current characteristic at 6 K. Fig. 20. Emission spectra in pulsed mode of several long wavelength IR surface plasmon QC lasers.
Fig. 21. Pulsed light output versus current characteristic of a \ = 24 «xm QC laser at various heat sink temperatures and voltage- current characteristic at 6 K. Fig. 20. Emission spectra in pulsed mode of several long wavelength IR surface plasmon QC lasers.
Fig. 22. Intensity profile of the surface plasmon mode for the \ = 21-4m QC laser with the double-surface plasmon (two metal claddings) waveguide. The mode is confined on both sides of the active regions by 300-nm-thick gold layers. The mode is completely symmetric in contrast to the single surface plasmon waveguide (active region sandwiched between a metal and a heavily doped n-type semiconductor region). The calculated optical confinement factor and waveguide losses are indicated by I and a, respectively.
Fig. 22. Intensity profile of the surface plasmon mode for the \ = 21-4m QC laser with the double-surface plasmon (two metal claddings) waveguide. The mode is confined on both sides of the active regions by 300-nm-thick gold layers. The mode is completely symmetric in contrast to the single surface plasmon waveguide (active region sandwiched between a metal and a heavily doped n-type semiconductor region). The calculated optical confinement factor and waveguide losses are indicated by I and a, respectively.
Fig. 23. Temperature dependence of the threshold current density fora \ = 21-j:m QC laser with a single-sided surface plasmon waveguide (squares) and with a metal-semiconductor- metal (double-surface plasmon) waveguide (circles). The arrow marks the low-temperature threshold current density of a \ = 21 ym laser with a metal-semiconductor-nt+ (double-surface plasmon). Insert: pulsed (30-ns pulse width, 100-kHz repetition rate) emission spectrum of a typical device. The spectrum was measured in rapid scan using a Nicolet Fourier transform IR spectrometer and a DTGS detector. The spectral resolution was set to 0.125 cm—?.
Fig. 23. Temperature dependence of the threshold current density fora \ = 21-j:m QC laser with a single-sided surface plasmon waveguide (squares) and with a metal-semiconductor- metal (double-surface plasmon) waveguide (circles). The arrow marks the low-temperature threshold current density of a \ = 21 ym laser with a metal-semiconductor-nt+ (double-surface plasmon). Insert: pulsed (30-ns pulse width, 100-kHz repetition rate) emission spectrum of a typical device. The spectrum was measured in rapid scan using a Nicolet Fourier transform IR spectrometer and a DTGS detector. The spectral resolution was set to 0.125 cm—?.
Related topics:
Digital ModulationMid-InfraredOptical physicsFar InfraredDiode LaserElectrical and Electronic EngineeringOptical WirelessMultimedia Data
580 California St., Suite 400
San Francisco, CA, 94104
© 2025 Academia. All rights reserved